Re: xpath improvement suggestion

Robert Haas wrote:

On Tue, Jan 5, 2010 at 6:09 PM, Arie Bikker arie(at)abikker(dot)nl wrote:


Hi all,

Well I had to burn some midnight oil trying to figure out why a construct
like
SELECT xpath('name()','a/');
doesn't give the expected result. Kept getting an empty array:
xpath
-------------
{}
instead of the expected "{a}"
BugID 4294 and the TODO item "better handling of XPath data types" pointed
in the right direction.
whithin src/backend/utils/adt/xml.c in the function xpath the result of the
call to xmlXPathCompiledEval is not handled optimally. In fact, the result
is assumed to be a nodeset without consulting the -type member of the
result. I've made some minor changes to xml.c to handle some non-nodeset
results of xmlXPathCompiledEval.
Essentially, the revised code makes an array of all the nodes in the
xpathobj result in case this is a nodeset, or an array with a single element
in case the reult is a number/string/boolean. The problem cases mentioned in
http://archives.postgresql.org/pgsql-hackers/2008-06/msg00616.php now work
as expected.
Revision of the code involves:
- A switch statement to handle the result type of xmlXPathCompiledEval.
- an additional function xmlpathobjtoxmltype.

diff of the revisioned code with respect to original is in attached file.

kind regards, Arie Bikker


Hi,

Could you please resend this as a context diff and add it to our patch
management application?

http://wiki.postgresql.org/wiki/Submitting_a_Patch
https://commitfest.postgresql.org/action/commitfest_view/open

Thanks!

...Robert

Hope this is the right attachement type (I'm new at this)

BTW. here a some nice examples:

- Get the number of attributes of the first childnode:

select ( xpath('count(@*)',(xpath('*[1]','a b="c"d e="f" g="j"//a'))[1]))[1];

- an alternative for xpath_exist('/a/d')

select (xpath('boolean(/a/d)','a b="c"d e="f" g="j"//a'))[1];

- fixes bug 4206

select xpath('//text()',xmlparse(document '?xml version="1.0"?elem1elem2one/elem2elem2two/elem2elem2three/elem2elem3att="2"//elem1'));

- fixes bug 4294

select xpath('name(/my:a/*[last()])', 'a xmlns="http://myns.com/ns"btext1/bctext2/c/a', ARRAY[ARRAY['my','http://myns.com/ns']]);

kind regards, Arie Bikker